How to Restore Gelcoat - Gelcoat Buffing
Gelcoat is a hard polyester resin coating that is applied over structural fiberglass to provide a smooth, glossy protective surface that improves appearance.
The outer surface of a fiberglass panel is normally a special resin called gelcoat. As the cometic component of the laminate gelcoat provides little structural value.
The typical thickness range of gelcoat a range is approximately 0.25 mm to 1 mm (0.010 inch to 0.040 inch), with a nominal thickness of around 0.5 mm (0.020").
When gelcoat is sprayed into a mold it takes on the shape and texture of the mold surface. The glossiness of gelcoat is due entirely to the highly polished, surface of the mold used in the manufacturing the panel.
Exposure eventually erodes the surface of gelcoat, leaving it dull and chalky. Fortunately, the gloss can usually be restored.
Before relying on the information below you should contact the manufacturer for recomendations for your specific RV. If that's not possible consult a auto body or RV tech. Also, a surface that looks like gelcoat may not be.
The first step in restoring the gloss to gelcoat is a thorough cleaning. A cup of detergent to a gallon of water is a good cleaning agent. If mildew is present, add a cup of household bleach to your cleaning solution. Difficult stains may require direct application of a concentrated cleaner formulated for fiberglass.
Rinse the clean surface thoroughly and let it dry.
For dependable results from wax or polish, the gelcoat surface must be free of oil and grease. After washing, wipe the surface with a rag soaked in MEK (preferred) or acetone, turning the rag often and replace it when you run out of clean areas. Protect your skin with thick rubber gloves.
On a new RV, routinely waxed gelcoat can retain its gloss for 15 years or more. The primary purpose of wax is to protect, but wax also has restorative properties.
You should follow manufacture's application instructions, but in general, wax is applied with a cloth or foam pad using a circular motion. Let the wax dry to a haze, then buff away the excess with a soft cloth. The remaining wax fills microscopic pitting in the gelcoat and provides a new, smooth, reflective surface.
Polish is not a coating, but rather an abrasive. Polishing removes the pitted surface rather than coating it. Use a soft cloth to apply polish to a small area at a time, rubbing with a circular motion until the surface becomes glassy. After polishing, you need to apply a coat of wax to protect the new surface and improve the gloss. Some polish products include wax in their formulations.
Using Rubbing Compound
If the gelcoat is weathered so badly that polish fails to restore its shine, you will need the corse abrasive of a rubbing compound.
Get a rubbing compound approved for fiberglass and apply it like polish, rubbing it with a circular motion until the surface turns glassy. The gelcoat on your RV is much thicker than paint so unless you get carried away the compound shouldn't cut all the way through. Simply be careful not to rub in one place too long. Keep in mind the RV may have been compounded previously.
After the surface has been compounded it needs to be polished to take out the course scratches left but the compound then a coat of wax should be applied. This process will restore the shine to gelcoat in almost any condition.
Using a Power Buffer
An electric buffer takes much of the work out of keeping your RV shining but when polishing and especially when compounding, you need to be careful not to abrade too deep. A buffer with an orbital motion will leave fewer swirl marks.
Electric buffers operate at relatively slow speeds, don't try to "make do" with a polishing bonnet fitted to a disk sander or chucked into a drill. You will probably ruin the gelcoat surface.
Gelcoat Restorer Products
There are a number of products on the market which claim to restore gelcoat. These products renew the gloss much like wax by fulling in the pits and making new smooth surface but don't require buffing. Results can be excellent, but they are an acrylic coating and can wear off and occasionally discolor. You usually have to apply multiple coats to get a good shine.
A multi-coat application can restore the shine to weathered gelcoat for up to a year, but when it is time to renew it, you will need to remove the old sealer using the special stripper supplied in the kit (or available separately). Apply five fresh coats of sealer and your boat should shine for another year.